Invasion of privacy is unwelcome; military invasion extremely so. Nectar consuming invaders in the floral domain are, however, a totally different matter.
As long as these invaders serve to transport pollen to their next flower landing (on the same species), they add value; analogous to the idea of the Greek philosopher, Heraclitus, who considered war a period of development between two periods of stagnation.
Should invaders eat the whole flower, the act would, of course, be unwelcome aggression as no seed would be produced. Loss incurred from invasion is the kind of offence people would run to the United Nations with. But flowers are largely pacifists with no whining tendencies (Manning, 2007; iSpot).